This application relates to Gurney flaps and more particularly to active Gurney flaps.
A Gurney flap is a small flat tab projecting from a trailing edge area of a wing. Typically the Gurney flap is set at a right angle to the pressure side surface of the airfoil, and projects up to 2% of the wing chord. The chord wise position is typically 0.9 chord to the extreme trailing edge when measured from the leading edge. This trailing edge device will improve airfoil lift.
The Gurney flap operates by increasing pressure on the pressure side of the wing that increase the lift force and may be used in auto racing, helicopter rotors, horizontal stabilizers, and high drag aircraft that take advantage of the resultant lift force.
The Gurney flap typically increases the drag coefficient, especially at low angles of attack, although for thick airfoils, a reduction in drag is known. A net benefit in overall lift to drag ratio is possible if the flap is sized appropriately based on the boundary layer thickness. Also, the increased pressure on the lower surface ahead of the flap means the upper surface suction can be reduced while producing the same lift.